This grant is to purchase and maintain a FACS IV cell sorter facility to be shared by a large number of research groups at Columbia University. The instrument is equipped for work in the ultraviolet, and for dual laser excitation. Among the systems which will be studied with the sorter are the uptake of histones by cells, mutants deficient in dihydrofolate reductase, and the role of IgM and IgD on lymphoblastoid cells. It is anticipated that sufficient time will be available on this instrument to cover the needs of a broad spectrum of potential users at Columbia University.